This study aimed at investigating the effect of Dynamic Assessment on vocabulary learning of Iranian EFL learners. Although it is widely acknowledged that this type of assessment can prove to be very effective for different aspects of language instruction, not much consideration has been given to DA of vocabulary. This study was an attempt to determine if DA procedures would improve students’ vocabulary learning. To this end, 40 female Iranian EFL learners were selected as participants of the study. They were of pre-intermediate level and their ages ranged from 18 to 25. The participants were assigned to control group who received new words by using the definitions and experimental group who learned new vocabulary items through DA procedures. The results of statistical analysis obtained from independent sample t-test and paired sample t-test, revealed that the experimental group outperformed the control group in post-test. This led the researcher to conclude that teaching vocabulary items through DA procedures can improve EFL learners’ vocabulary learning. As a result, the findings of the study may have some pedagogical implications in language teaching, and help EFL teachers to employ DA procedures in teaching vocabulary items in their classes as an effective way of improving the students’ vocabulary learning.